Combined volume and selectivity control device



NOV' 6, 1945. A. D. zAPPAcosTA 2,388,590

COMBINED VOLUME AND SELECTIVITY CONTROL vDEVICE Filled June 29, 1942 T`TORNEY l Patented Nov. 6, 1945 COMBINED VOLUME SELEQ'EEVITY n CONTROL DEvroE Amedeo D. Zappacosta, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application June 29, 1942, Serial No. 448,940

(Cl. Z50-20) 7 Claims.

.My present invention relates to control devices for radio receivers, and more particularly to a radio receiver adapted to have its output level and selectivity concurrently controlled.

One of the main Objects of my present invention is to provide a novel `and simplified method of, and means for. concurrently adjusting the radio frequency amplifier gain and selectivity of a radio receiver.

,Another important object of my invention is to provide in the tuned radio frequency amplifier section of a .radio receiver a device for simultaneously controlling the gain of one amplifier stage and the shape .of the ,response curve of another .amplifier stage.

Another important object of this invention is to `provide .in association with at least two cascaded tunedradio frequency amplifiers a volume control .device'capable of `adjusting the gain of a later amplifier, and adjustment of the aforementioned `,gain causing a second device to be operative to alter the selectivity of an earlier amplifier.

Another object of the invention is to provide across the tuned input circuit of a radio frequency amplifier of la radio receiver a selectivity control diode whose conductivity is a function of the adjustment of the volume control device of a tuned radio frequency amplifier which follows the first mentioned amplifier.

Still other objects of the invention are to improve generally the simplicity and eiciency of volume-selectivitycontrol devices for high frequency receiving equipment, and more especiallyvto provide such control device in a readily manufacturable and economical manner.

The novel features which I believe to be characteristic of myinvention are set forth with particularity inthe appended claims; the invention itself, however, as to both its organization and method of operation will best be understood'by reference to the following description takenin connection with the drawing in which l have indicated diagrammatically a circuit organization whereby my invention maybe carried into effect.

in the drawing:

1 shows a vcircuit diagram of a portion of a radio --recei-ver -embodying the invention,

Fig. 2 "shows the effect ofthe invention on the selectivitlr of thecontrolled ampli'er,v

by numerals I vand Z. While each of these tubes is shown as of the pentode type, itis to be under- Fig. 3 graphically shows the effect of the selectivity control diode on .the impedance ofthe resonant input circuitof the controlled amplifier. Referring fnow toFig. 1, there is shown .a pair of casceded radio-frequency amplifiers designated stood that any other types of tubes may be eniployed. The tube I may be a GAB? type of tube, While tube 2 may be a 6SJ7. However, this invention is in n o way restricted to the nature of the tubes to be employed. I'he signal input grid 3 of tube I is shown connected to a high yfrequency signal pick-up device A which has the high potential lside thereof connected to grid 3 through a vradio frequency coil 5 arranged in series with a coupling condenser l. The adjustable tuning condenser I is connected between the junction of coil '5 and condenser 6 and ground. Hence network :5f-Tl functions as the tunable input `circuit of the amplier I.

, The signal pick-up device ,4 preferably has an impedance of the order of ohms, although it is to be understood .that this value is purely illustrative. The coil 5 preferably has a voltage stepup ratio of about 2 0, but here, again, this constant is merely given by way of illustration. The plate 8 of tube I is connected to an intermediate point on the coil 9 of the following tuned circuit. This is done to increase the selectivity of the tuned circuit. The coil 9 is shunted by the adjustable condenser ,lll. Network S-Ill is, of course, tuned to the same high frequency to which circuit ,i-'I is tuned. rIhre low alternating potential side of the network .fl-I0 is connected to ground for high frequency currents. The screen grid electrode of tube I is connected by lead lII to the low alternating potential end of coil 9, and both the plate and screen grid of tube I will be connected to the plus 250 volts terminal of the direct current lsource of the receiving system.

vJT-he cathode of tube I may `be connected to ground through the usual bypassed biasing resistor t2, the grid 3 being connected to ground through the grid return resistor I3. The following amplifier -2 has its control grid I4v coupled to the high alternating potential side of its resonant input circuit 9--I0 through the coupling condenser I5.. The control grid Itis returned to ground through the grid return resistor l5. The plate and `screen grid of tube 2, as inthecase of tube I, are connected respectively to an intermediate point andthe lower end of the following 4coil `9". The adjustable tuning Acondenser Ill shunts coil 9', and Ytimes the latter -to the samehigh frequencyvavs -the preceding high Vfrequency circuits are tuned'to. The lower end of coil 9 will also be connected to the plus 250 `volt terminal of the energizing current source of the receiver.

, The ,voltage supply resistor, which is connected in the usual manner across the direct current source of a receiving system, is shown as comprising four sections designated by the numerals I'I, I8, I9 and 2U. The left hand terminal of resistor 20 is established at ground potential, while the right hand end of resistor II is connected to provide the plus 250 volt potential point referred to previously. The cathode 2l of tube 2 is connected by lead 22 and an adjustable tap 23 to sectionA I8 of the voltage supply potentiometer. The adjustable tap 23 constitutes the volume control device which is adjusted between minimum and maximum volume points as indicated inFig. 1. When the tap 23 is adjusted to the right hand end of resistor section I8, the bias of the control grid I4 of tube 2 is a maximum, andaccordingly the gain of tube 2 is a minimum. This results in the volume output level of the receiving system being a minimum. Conversely, when tap 23 is adjusted to the left hand end of resistor section I8, the negative bias on grid I4 is av minimum with the result that the receiver output level is a maximum.

The selectivity control device may consist of a diode 30. This can b'e a 6I-I6 type tube whose anodes are strapped together, and are connected by lead 3| to the high alternating potential side of the tuning condenser 'I. The cathodes of tube 30 are connected together, and the lead 32 connects them to the junction of resistor sections 20 and I9. The said junction is bypassed to ground by a condenser 40 having a magnitude of approximately 0.5 micro-microfarads (mmf.). This magnitude is purely illustrative. Merely by Way of illustration, it is also pointed out that resistor section I'I may have a magnitude of 47,000 ohms; resistor section I8 may have a magnitude of 5,000; resistor section I9 may have a magnitude of 1,000 ohms; and section 20 may have a magnitude of 150 ohms.

It will now be seen that the diode 30 acts as a shunt impedance across the tuned input crcuit 1. The delay bias on diode 30 varies inversely with the Vnegative bias on grid I4. It is to be understood that the signal pick-up device l4 includes Within it a conductive path to ground so that the diode anode returns to ground. In Ythe absence of signal energy the potential difference between the anode and cathode of the diode 30 depends upon the potential of the junction of resistor sections and I9. The potential of that junction point, in turn, depends upon the adjustment of tap 23 on resistor section I8. This will be obvious from the fact that the space current of amplier 2 flows through lead 22V and tap 23 to the voltage supply network.

Generally speaking, the resonance curve of input circuit 5 1 will assume the shape shown by the full line curve of Fig. 2 when Weak signals are received. This can be readily seen from the fact that for weak signal reception the adjustable tap 23 will be adjusted along resistor sectionv I8 to the'maximum setting. In that adjustment of the volume control tap 23 the eiective negative bias on grid I4 of amplier 2 is a minimum with the result that the space current flow through lead 22 is a maximum. Hence, there will be an increase of current flow through the resistor sections I9 and `20 to ground. This means that the cathode of diode 30 becomes increasingly positive with respect to the diode anode. Therefore, the delay bias Von the diode anode is a maximum. For example, let it be assumed 2,388,590 Y... 'f ,c

sonthat interference effects aremore radily disl criminated against. Noises are readily reduced when the input circuit 5 1 has high selectivity.

Conversely, when the received signal strength is of a high level, the volume control tap 23 is adjusted to the minimum volume setting of resistor section I8. This causes a reduced cathode current iiow through lead 22. The eiective delay bias of diode is reduced. Fig. 2 shows the round topresonance curve shown in dotted line which results for strong signal reception when the effective delay bias of -0.15 volts is produced on the diode 30. 1

Fig. 3 shows how the impedance of the tuned circuit 5 1 decreases towards 25,000 ohms (equals QwL, where Q=1) as a minimum' as the delay bias of diode 30 is decreased. It will lbe understood that when the delay bias of diode '3D is a minimum, then the receivedv signal amplitude will be sufficient; to override the minimum rbias and render diode 30 conductive.; When diode 30 is conductive it has a minimum impedance, and',

therefore, presents maximum equivalent series damping impedance to the tuned circuiti-JI. The broadened resonance curve'is therefore produced.

At maximum setting of tap 23 the diode 30 looks like a shunt capacitor acrosscapacitor 1,

because it is non-conductive. The circuitimpedance of 5 1 is equal to QwL. When the diode becomes conductive it acts like a variable resistor shunted across the tuned circuit. The more conductive the diode becomes, the lower the tuned .Circuit impedance because the Q ofthe tuned Icircuit is lowered. When receiving weak signals the delay bias on diode 30 is minus 1.5 volts. This means that a weak signal must develop at least a A peak voltage of 1.5 volts across coil 5. With an antenna gain of 20 in the tuned circuit, .the weak signal must be equal to approximately 53,000 microvolts'which is considered' a strong signal because one microvolt `Will give full receiver output.

It will, therefore, be appreciated that concurrently with the adjustment of thevolume control instrumentality there'is `secured a simultaneous change in the selectivityandattenuation of the input circuit 5 1. For-'strong signal reception', the volume control device 'is adjusted to decrease the gain of amplifier 2. Simultaneously the input circuit 5 1 is dampened to increase'the attenuation of signals and decrease selectivity.v Selectivity may be reduced in that`case',.because the signal level will be suiiicient to override any inter-v ference or noise eifects. The reverse is true inthe case of weak signal reception, because in that case' the gain of amplifier 2'Ji's increased with concurrent increase in selectivity of input circuit 5 1.

It is to be understood that the circuits'S-f-vl, 9 I0, and 9 I0 are each tuned to the common carrierfrequency of thesignals. Furthermore, the volume control device may be located in the intermediate frequency amplifier ofl A a superheterodyne receiver, or it may ,even bey located, in the cathodey circuit of an audio frequencyamplifier. The essential requirement is .that the diode 30 have its effective delay `biasv varied in 4accord- 1 ance with variations in gainof vthe amplifier, subenough to permit maximum sensitivity on'weak signals, and to prevent diode 30 from becoming conductive. It is, also, pointed out that a p-lurality of selectivity control diodes may be inserted across cascaded resonant selective circuits.

It will now be seen that I have provided a novel method of changing the input selectivity when the volume control is adjusted from setting to setting. In this way I can decrease the time constant of the input circuit -1 so that the receiver will quickly recover after being subjected to excessive signal input voltages. It will also be noted that it is possible to increase the radio frequency attenuation over the amount controlled by volume control 23. With large signal input voltage up lto 250 volts the diode 3|) acts to prevent this input voltage from building up to a value equal to Q times 250 volts by making Q drop to unity. Then, the 250 volts is dropped across the reactance of coil 5 which limits the current taken by diode 30.

While I have indicated and described a system for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular u organization shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended claims.

What I claim is:

1. In a high frequency receiving system, a rst amplifier tube provided with a selector circuit, a diode connected in shunt across said selector circuit, at least a second amplifier tube provided with input electrodes and output electrodes, a second selector circuit coupling the rst amplier tube to the input electrodes of the second amplifier tube, a direct current voltage energizing network common to the space current paths of said diode and second amplifier tube, and means connected to said energizing network and located in the space current path of said second amplifier tube for regulating the space current iiow'of said second amplifier tube between predetermined maximum and minimum values whereby the second tube amplification is varied over a relatively wide range thereby automatically to adjust the conductivity of said diode over said range.

2. In a high frequency system, a first electron discharge device provided with a resonant circuit, means having variable conductivity operatively connected to said resonant circuit for controlling the selectivity thereof, a second electron discharge device having input electrodes and output electrodes, means coupling the input electrodes of said second device to said irst device, a variable resistor arranged in the space current path of the second device for adjusting the space current flow of the second device over a relatively wide range thereby to provide a gain control instrumentality, and said means of variable conductivity including a connection to said space current path of the second device whereby adjustment of the effective magnitude of said gain control resistor causes changes in conductivity of said variable conductivity means thereby to vary the selectivity of said resonant circuit,

3. In a high frequency receiving system, a rst amplier tube provided with a selector circuit, a diode connected in shunt across said selector circuit, at least a second amplifier tube provided with input and output electrodes, a direct current voltage energizing network common to the space current paths of said diode and second amplier tube, and means connected to the energizing network and located in the space current path of said second amplifier tube for regulating the space current ow of said second amplier tube and its amplification thereby automatically to adjust the conductivity of said diode.

4. In combination with a selector input circuit, a device of unidirectional conductivity operatively associated with said selector circuit to control the selectivity thereof, an amplier tube following said input circuit, and a potentiometer including a manually adjustable element common to the space current path of said amplifier tube and said device of unidirectional conductivity for rendering the conductivity of such device dependent upon relatively wide changes in space current of said amplifier tube.

5. In a high frequency receiving system, a first amplifier tube provided with a selector circuit, a diode connected in shunt across said selector circuit, at least a second amplifier tube provided with input electrodes and output electrodes, a secondselector circuit coupling the rst amplifier tube to the input electrodes of the second amplier tube, a direct current voltage energizing network common to the space current paths of said diode and second amplifier tube, and an adjustable potentiometer connected in circuit with the energizing network and located in the space current path of the second amplifier tube for regulating over a relatively wide range the space current flow of said second amplier tube and its amplification thereby automatically to adjust the conductivity of said diode.

6. In a high frequency system, a first electron discharge device provided with a resonant circuit, a control electronic device having variable conductivity operatively connected to said resonant circuit for controlling the selectivity thereof, said control electronic device acting like a capacitor when non-conductive, a second electron discharge device having input electrodes and output electrodes, means coupling the input electrodes of said second device to said iirst device, a potentiometer including a manually adjustable element arranged in the space current path of the second device for adjusting the space current flow of the second device over a relatively wide range thereby to provide a gain control instrumentality, and said control electronic device of variable conductivity being operatively connected to said space current path of the second device so that adjustment of said gain control instrumentality causes changes in conductivity of said control electronic device thereby to vary the selectivity of said resonant circuit.

7. In combination, a rst tube provided with a resonant circuit, a diode operatively connected to said resonant circuit for controlling the selectivity thereof, a second tube having input electrodes and output electrodes, means coupling the input electrodes of said second tube to said rst tube, means arranged in the space current path of the second tube for adjusting the space current iiow of the second tube between relatively widely spaced minimum and maximum values thereby to provide a volume control instrumentality, and said diode being operatively connected to said space current path of the second tube so that adjustment of said volume control instrumentality causes changes in conductivity of said diode thereby to vary the selectivity of said resonant circuit.

AMEDEO D. ZAPPACOSTA. 

